High signal magnetic resonance (MR) images of void spaces, notably the lungs, have been acquired using laser-polarized or hyperpolarized noble gases, such as Xenon-129 and/or Helium-3. (See, U.S. Pat. No. 5,545,396, the entire content of each being expressly incorporated hereinto by reference, and References 1-4). Xenon-129 has also been used as a probe for blood, muscle, and brain tissue. (References 5-7). These studies rely on xenon dissolving in a carrier, such as lipid vesicles or blood. Since helium is 10-100 times less soluble than xenon in such materials (Reference 8), Helium-3 has been used exclusively for imaging air spaces. However, considering that the signal of Helium-3 is over 10 times greater than that of Xenon-129 for presently attainable polarization levels, it would be highly desirable to discover some means by which Helium-3 could be introduced into the vascular system. According to the present invention, such means are provided.
Broadly, the present invention is embodied in introducing a hyperpolarized noble gas (e.g., Helium-3 and/or Xenon-129) into a human or animal vascular system in the form of an injectable liquid containing microbubbles of the hyperpolarized gas dispersed or suspended in a biologically compatible carrier liquid. The techniques of the present invention allow for a potential increase in signal, and absence of background thereby permitting high resolution MR images to be obtained of human or animal vascular systems (i.e., angiographic images).
These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follow.